An electro-osmotic pump is a pump using the principle that a fluid moves due to electro-osmosis occurring when a voltage is applied to both ends of a capillary or a porous membrane by using electrodes, and unlike ordinary pumps, the electro-osmotic pump is advantageous in that it causes no noise since it has no part that mechanically operates, and can effectively control a flow rate in proportion to the voltage applied.
A conventional electro-osmotic pump uses chemically stable platinum as an electrode material. When an aqueous solution is used as a fluid, a reaction in a positive (+) pole is as shown in Reaction Formula 1 below, and a reaction in a negative (−) pole is as shown in Reaction Formula 2 below.2H2O→O2+4H++4e−  [Reaction Formula 1]2H2O+2e−→H2+2OH−  [Reaction Formula 2]
According to Reaction Formula 1, an oxygen gas resulting from an oxidization reaction of water is continuously generated in the positive (+) pole; and according to Reaction Formula 2, a hydrogen gas resulting from a reduction reaction of water is continuously generated in the negative (−) pole.
The movement of electrons and ions as a result of the oxidization reaction and the reduction reaction is an essential phenomenon to continuously move a fluid in the electro-osmotic pump. When the electro-osmotic pump is embodied by using the platinum electrode as described above, there is difficulty in practically using the pump since it is difficult to realize a stable flow rate due to the phenomenon that the gas generated by the oxidization and reduction reactions is caught in small pores of a porous membrane, and it is difficult to realize closed-loop due to a safety problem causing from the simultaneous and continuous generation of the oxygen gas and the hydrogen gas within the fluid.
Further, in case of the electro-osmotic pump using the platinum electrode, since water of the moving fluid participates in the oxidization and reduction reactions, and the platinum as an electrode material does not participate in the reactions and is only used as an electrode causing the oxidization and reduction reactions of water, the electrode is maintained. In this case, the platinum electrode is called a non-consumable electrode. The electro-osmotic pump, which stably and safely operates without generating gas, can be achieved if an electrode material is made by using a reaction that generates no gas. For example, in case of using a silver/silver oxide electrode reaction, a reaction in the positive (+) pole is as shown in Reaction Formula 3 below, and a reaction in the negative (−) pole is as shown in Reaction Formula 4 below.2Ag(s)+H2O→Ag2O(s)+2H+2e−  [Reaction Formula 3]Ag2O(s)+2H+2e−→2Ag(s)  [Reaction Formula 4]
In the positive (+) pole, an oxidization reaction of silver according to Reaction Formula 3 occurs, and in the negative (−) pole, a reduction reaction of a silver oxide according to Reaction Formula 4 occurs. In this case, the electrode acts as a material participating in the electrode reactions, rather than a means for simply applying a voltage. If this consumable electrode is applied to the electro-osmotic pump, a volume of a fluid that can be moved by the electro-osmotic pump is restricted due to the limited amount of the electrode material.
Therefore, it is impossible to safely and stably move a large volume of a fluid without generating gas for a long period of time by using the conventional electro-osmotic pump. In other words, the electro-osmotic pump, to which the consumable electrode reaction is applied, has had a problem in that due to a limited amount of an electrode active material, the pump is suitable for moving a small volume of a fluid in one direction one time by means of an electrode reaction that can be realized with the small value of the fluid, but is not suitable for continuously moving a large volume of a fluid.